1. Field of the Invention
The present invention relates to a lifting jack arrangement for lifting platforms for vehicles.
2. Discussion of Related Art
Such lifting jack arrangements are preferably used for under-floor motor vehicle lifting platforms comprising one or more jacks. Each lifting jack comprises a dimensionally stable steel tube having a circular or polygonal cross-section which is guided in a sleeve, usually arranged at floor level. The sleeve is vertically moved from an initial position at floor level into an elevated operational position by suitable lifting means, usually a hydraulic cylinder positioned inside the tube.
A support construction for the vehicle to be lifted, which may comprise flat drive-on supports with swiveling telescope arms provided with carrying elements at their ends or the like, is attached to the upper end of the guide tube. In such lifting jack arrangements the outer sliding surfaces of the guide jacks which interact with the sliding elements in the sleeves are typically hard chromium plated to perpetuate the required sliding properties over several years of use. To obtain the required permanent attachment of the chromium layer and to prevent wear of the sliding surfaces, first a thin metal layer, for example nickel, is applied to the outer surfaces of the guide jacks before the hard chromium layer is applied by known methods. However, such a coating is technically complicated and expensive.